CoCoRaHS

CoCoRaHS is a unique, non-profit, community-based network of volunteers of all ages and backgrounds working together to measure and map precipitation.

Wednesday, August 6, 2008

Edouard Could Have Been Worse

T.S. Edouard did little if any damage to Texas and Louisiana. It did bring some moderate to heavy rainfall with a little minor flooding.

The Houston/Galveston area saw 2-5 inches of rainfall with a few 6-7" reports out there. So far this morning the biggest CoCoRaHS report I have seen is 5.03 inches in Jefferson County, TX -- not too far from the towns of Orange and Sabine Pass.

That's a great rainfall -- a bit much, but it can certainly be handled by that part of the world.

Here in the west we would have seen some serious flash flooding and damage from an event like that.

The remnants are compact but are bringing some much needed moisture as it passes through north-central Texas.

The Dallas area awoke to humid but overcast skies with breezy conditions this morning -- a welcome relief from the streak of 100 degree temps.

I was watching The Weather Channel last night before bed and the on-camera meteorologist made an interesting observation.

This HUGE high pressure and bubble of hot dry air that has been parked over the southern plains actually protected Texas and Louisiana from a more serious storm.

The circulation around the high pressure (clockwise) actually steered the storm on a nearly due west-northwest path across the top of the Gulf of Mexico.

But it also fed a lot of that hot, dry air into the storm as well.

This kept Edouard from really ever organizing into something potentially large. Had that hot, dry air not been in place, the warm waters could have easily allowed Edouard to rapidly increase in size and strength.

TODAY's LESSON

So yesterday we talked about the layers of the atmoshpere and I said we live in the lowest layer, called the troposphere, which is approx. 7 miles above the surface.

And although the overall temperature trend is to decrease with height, you will find small layers where pockets of warmer temperatures can be found and this helps to drives our weather.

The rate of cooling as you go up is called the lapse rate.

As you picture the atmosphere, you have to think vertically, or 3-D, so mentally picture anything that helps. (i.e. stacking blocks)

Once you reach the top of the troposphere, the lapse rate becomes zero, meaning the temperature stops decreasing with height and becomes constant with height.

This region is called an isothermal (or an equal temperature zone). The bottom of this new layer marks the end of the troposphere and the beginning of the second layer in our atmosphere, which is called the stratosphere.

The boundary that seperates the two layers is called the tropopause.

The tropopause, or trop (with a long O sound) in weatherman lingo, is important to meteorologists because it's height varies with both season and location.

It also helps identify the jet stream, which is the fast river of air current that circles the globe and drives weather patterns.

So now that we are into the stratosphere,the beginning of it marks a layer with constant temperature as you increase in height, between about 7-12 miles above the surface.

Then the temperature begins to warm with height, which is called a temperature inversion. The inversion is deep, meaning the layer where temperature warms is several miles up.

This does a few things...it acts like a giant cap and keeps the troposphere locked in about the lowest 7 miles. It prevents stratospheric air from mixing down into the troposphere (obviously there could be a little mixing where the two layers meet at the tropopause, but it isn't significant).

Now even though the temperature is warming with height in most of the stratosphere, it is still extremely cold, averaging less than -46°C.

The layer of warmer air in the stratosphere is due to the gas ozone retaining heat.

At the top of the stratosphere, you will find the stratopause, which is the boundary between the 3rd layer of atmosphere called the mesosphere (middle sphere).

Air at this level is VERY thin and pressure is quite low, averaging about 1 mb. (compared to 1013.25 mb at sea level)

Nitrogen and oxygen levels here are about the same as found at sea level, but you couldn't survive long breathing without proper equipment. The brain would experience hypoxia, meaning it would become oxygen starved.

There is little ozone in this layer so after a small transition of air temperature remaining constant with height, the temperature once again starts to decrease with height.

In the mesosphere, Earth's atmosphere reaches it lowest overall average value of -90°C.

At the top of the mesosphere is the mesopause, marking the transition to the 4th and highest layer of our atmosphere, the thermosphere.

As it transitions the temperature goes back to constant with height then starts to increase with height until reaching space.

The mesosphere is known as the hot layer. Here the oxygen molecules absorb solar energy. Temperatures actually vary from day to day depending on solar activity.

The air here is actually too thin to measure temperature with a thermometer, but it can be determined by observing the orbital change of satellites caused by the drag of our atmosphere.

At the very top of the mesosphere you will have reached the top of our atmosphere, an area where molecules shoot off into space. This region is sometimes called the exosphere. (exiting the atmosphere)

WOW! We got through all the layers of the atmosphere.

Below is a link to a website with a little more information AND a graph that shows the temperature profile from the ground to the top, putting all this information together visually for you.